DR.TANVIR-UL-HASSAN DAR

ASSISTANT PROFESSOR

DEPARTMENT OF BIOTECHNOLOGY

SCHOOL OF BIOSCIENCES AND BIOTECHNOLOGY

SEMESTER: 2ND

COURSE CODE:Mib-2014

COURSE TITLE: MICROBIAL GENETICS AND MOLECULAR BIOLOGY

Unit:5 MICROBIAL:MECHANISM OF GENETIC

VARIATION.

5.1 Mutation and their chemical basis

Mutation

Introduction • Sudden heritable change in genetic material or character of an organism is

known as mutation

• Individuals showing these changes are known as mutants

• An individual showing an altered phenotype due to mutation are known as

variant

• Factor or agents causing mutation are known as mutagens

• Mutation which causes changes in base sequence of a gene are known as

gene mutation or point mutation

History

• English farmer Seth Wright recorded case of mutation first time in 1791 in

male lamb with unusual short legs

• The term mutation is coined by Hugo de Vries in 1900 by his observation

in Oenothera

• Systematic study of mutation was started in 1910 when Morgan

genetically analyzed white eye mutant of Drosophila

• H. J. Muller induced mutation in Drosophila by using X- rays in 1927 ; he

was awarded with Nobel prize in 1946

Characteristics of Mutation • Generally mutant alleles are recessive to their wild type or normal alleles

• Most mutations have harmful effect, but some mutations are beneficial

• Spontaneous mutations occurs at very low rate

• Some genes shows high rate of mutation such genes are called as mutable

gene

• Highly mutable sites within a gene are known as hot spots.

• Mutation can occur in any tissue/cell (somatic or germinal) of an organism

Classification of mutation

• Based on the survival of an individual

1. Lethal mutation – when mutation causes death of all individuals undergoing

mutation are known as lethal

2. Sub lethal mutation - causes death of 90% individuals

3. Sub vital mutation– such mutation kills less than 90% individuals

4. Vital mutation -when mutation don’t affect the survival of an individual are

known as vital

5. Supervital mutation – This kind of mutation enhances the survival of

individual

• Based on causes of mutation

1. Spontaneous mutation-

Spontaneous mutation occurs naturally without any cause. The rate of spontaneous mutation is very slow eg- Methylation followed by deamination of cytosine.

Rate of spontaneous mutation is higher in eukaryotes than prokaryotes.

Eg. UV light of sunlight causing mutation in bacteria

2. Induced Mutation-

Mutations produced due to treatment with either a chemical or physical agent are called induced mutation .

The agents capable of inducing such mutations are known as mutagen.

use of induced mutation for crop improvement program is known as mutation breeding.

Eg. X- rays causing mutation in cereals

•

1. Somatic mutation-

A mutation occurring in somatic cell is called somatic mutation.

In asexually reproducing species somatic mutations transmits from one

progeny to the next progeny

2. Germinal Mutation-

When mutation occur in gametic cells or reproductive cells are known as

germinal mutation.

In sexually reproductive species only germinal mutation are transmitted to the

next generation

Based on tissue of origin

• Based on direction of mutation

1. Forward mutation- When mutation occurs from the

normal/wild type allele to mutant allele are known as forward

Mutation

2. Reverse mutation- When mutation occurs in reverse

direction that is from mutant allele to the normal/wild type allele

are known as reverse mutation

• Type of trait affected

1. Visible mutation- Those mutation which affects on

phenotypic character and can be detected by normal

observation are known as visible mutation

2. Biochemical mutation- mutation which affect the

production of biochemicals and which does not not show any

phenotypic character are known as biochemical mutation

Chromosome Mutations

• May Involve:

– Changing the structure

loss or gain

Chromosome Mutations

• Five types exist:

–Deletion

–Inversion

–Translocation

–Nondisjunction

–Duplication

Deletion

• Due to breakage

• A piece of a chromosome is lost

Inversion

• Chromosome segment breaks off

• Segment flips around backwards

• Segment reattaches

Duplication

• Occurs when a gene sequence is repeated

Translocation

• Involves two chromosomes that aren’t homologous

• Part of one chromosome is transferred to another chromosomes

Translocation

Nondisjunction • Failure of chromosomes to separate during meiosis

• Causes gamete to have too many or too few chromosomes

• Disorders: – Down Syndrome –

– Turner Syndrome –

– Klinefelter’s Syndrome –

Chromosome Mutation Animation

Types of Gene Mutations • Include:

–Point Mutations

–Substitutions

–Insertions

–Deletions

–Frameshift

Point Mutation • Change of a single

nucleotide

• Includes the deletion, insertion, or substitution of ONE nucleotide in a gene

Point Mutation

• Sickle Cell disease is the result of one nucleotide substitution

• Occurs in the

hemoglobin gene

Frameshift Mutation

• Inserting or deleting one or more nucleotides

• Changes the “reading frame” like changing a sentence

• Proteins built incorrectly

Gene Mutation Animation